package org.jiajie.coffeecodes.concurrent.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * @author jie
 * @date 2021/9/29 10:14 PM
 */
public class Mutex implements Lock {
    // 静态内部类，自定义同步器
    private static class Sync extends AbstractQueuedSynchronizer {
        /**
         * 是否处于占用状态
         */
        @Override
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }

        /**
         * 当状态为0的时候获取锁
         */
        @Override
        protected boolean tryAcquire(int acquires) {
            if (compareAndSetState(0,1)) {
                setExclusiveOwnerThread(Thread.currentThread());
            }
            return false;
        }

        /**
         * 释放锁，将状态设置为0
         */
        @Override
        protected boolean tryRelease(int release) {
            if (getState() == 0) throw new IllegalMonitorStateException();
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        /**
         * 返回一个Condition，每个condition都包含了一个condition队列
         */
        Condition newCondition(){
            return new ConditionObject();
        }
    }
    // 仅需要将操作代理到Sync上即可
    private final Sync sync = new Sync();
    @Override
    public void lock() {
        sync.acquire(1);
    }
    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }
    @Override
    public void unlock() {
        sync.release(1);
    }
    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }
    public boolean isLocked(){
        return sync.isHeldExclusively();
    }
    public boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }
    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }
    @Override
    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }
}
